For tracing 'signal' in DIY builds .. especially if one is 'directly probing' [ie the DIY 'prob-ulator' concept], I do recommend something fairly cheap.
If one is brave enough to venture to probing higher voltages, meaning larger ac audio signals and possibly [often!] in the presence of dc voltages a 'cheap-ish' audio interface is best.
One wouldn't be 'ping-ing' their expensive interface with some hokey 'probe' planted in some 'unknown diy', for example.
lol the 'Lady and the Tramp' scenario ;D
For cheap, I like [personally] M-Audio stuff on the PC - they do do Mac as far as I know.
I use a 'four analog i-o plus two digital' in this role ... one channel of i-o for 'loopback reference', one channel for 'device under test' (send and return to your DIY) .. all balanced preferably.
The other stereo analog i-o is good for 'monitoring' [ie. for playing media while you go, completely seperate from the testing]
And a stereo digital pair of i-o is good for independant 'digital perspectives'.
I use M-Audio Pro 610 Firewire .. I think with change from said hundred dols us. But it could be anything you like.
Basically cheap, with something like at worst, 0.015% THD+N at near full-scale output and with a 'hum floor' of around 120 dB [below said near full-scale output]. Most do way better, of course .. but this is the 'cheap' seats.
I find they do around 10Vpp or so input and/or output .. at near full-scale levels with said level of distortions, before really borking out.
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So that would be i) cheap ii) balanced iii) sufficient I-O
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For stuff like discrete circuits at +24V supply, I think it does pay to make your own DIY 'prob-ulator'
It is basically a probe with a dc blocking cap [to block dc!] and a parallel resistance of some moderately high Mohm value [to not load down your 'signal under test'].
Better ones go into an 'attenuator box' to conveniently 'match' or 'map' your 'ac signal under test' to your interface 'available signal range Vpp'.
Again, it's more complicated to describe than to do. Once you get going, it's a breeze and you can probe at will without fear of the 'troubles'.
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In R E W that means HD quality signal send, and return which can be 'visualised' in 'near real time' and mostly without 'glitches'
ie. spectral analysis, sweep analysis and quite groovy 'CRO' type voltage waveform measurement.
This relatively 'new' feature of R E W is far, far more accurate and with much greater resolution than my trusty Tektronix 4chn CRO [analog cro with digital control and fab measurement cursors].
I don't even want to mention the flexible 'triggering', nicely done 'deep trace buffer' [for the voltage waveform capture] or the attendant 'after the fact' [historical ] voltage waveform visualisation capabilities. 8) - they are something else .. along with available 'trace math' functions on the dual channels casually at one's disposal.
The accuracy is superb ... it eats up signal levels of even few fractions of micro-Volts peak-to-peak.
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Reliability, in terms of the mundane things like 'crashes' is legendary and is a proper and fitting testimony to the rock solid stability ... no crashee or bsods here thanks muchly!
As I alluded to previously [befoor] - I like to play media [at the same time, on the same computer] whilst I'm doing all this .. for many long hours at a stretch .. usually Art Bell's Coast-to-Coast radio broadcasts from wayback, with really interesting peoples, like mr Graham Hancock and similar.
[circa 2016 amd 8-core box , win7_64, lotsa mem and SSDs and about 140VA of power used with a 23" Samsung monitor]
No probs whatever. Same with browsing the net, or even most network file operations going on too.
And finally, install/un-install/upgrades processes are almost 'a pleasure - ' it's so quick and 'lightweight' - haven't yet had to 'step back' even once on any revision in all the years of REW.
Even so to the point where REW is a fine 'benchmark' app for audio subsystems - I use it to 'stress test' wannabe audio PCs
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That's basically it. Carry on
